This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The primary goal of project is to understand the mechanisms of sex differentiation in primordial germ cells (PGCs), the embryonic cells that give rise to either sperm or egg cells in the adult. Current evidence suggests that PGCs in both female (XX) and male (XY) embryos begin life being bipotent, capable of differentiating along either the male or female pathway. The decision to differentiate to male or female germs cells is controlled by the gonadal somatic cells, the cells that surround the PGCs. But this has not been fully tested. After sex differentiation, male and female germ cells alter their DNA and begin cell division based on whether they have entered the male or female specific pathway. These sex-specific events are essential to produce functional sperm and eggs. Otherwise, normal fertilization and embryonic development do not occur correctly. However, we do not know the exact relationship between sex differentiation and the following sex-specific events in fetal germ cells. Our previous data demonstrate that in mice by 13.5 days after fertilization, PGCs control their own fate, and are no longer regulated by the surrounding somatic cells. In this project, we will first examine the relationship between sex differentiation and the following sex-specific events in germ cells cultured with external chemicals/factors. Next, we will test which conditions, if any, are required to direct PGCs into male or female pathway. Finally, we will determine if germ cells maintain intrinsic clock to enter meiosis by themselves in the absence of somatic support.